1. Field of the Invention
The present invention relates to a display medium, and more particularly to a display medium including two or more display elements that have been stacked together.
2. Description of the Related Art
Display mediums from two or more display elements that have been stacked together have been proposed. At the external terminal connection portions of such layered form display mediums, in order for the lead lines from the pixel portion (functional area) of the display elements to be each individually connected to the outside of the pixel portion, patterns are adopted in which, for example, the end portions of the stacked display elements project out from each of the substrates, the end portions of the stacked display elements are disposed in a step shape, or the like (see, for example, Japanese Patent Application (JP-A) Nos. 2001-42353, 2002-297050).
FIG. 16 is an example of a configuration of external terminal connection portions in a conventional layered form display medium and is a partial cross-section showing schematically a display medium of three stacked display elements (100a, 100b and 100c). In FIG. 16, lead lines 102a, 102b and 102c are, respectively, formed to lead from display regions (not shown) in substrates 101a, 101b and 101c in the display elements 100a, 100b and 100c, and external connection relay substrates 103a, 103b and 103c, for electrically connecting pixel portions to the outside, are connected to the respective lead lines 102a, 102b and 102c. 104a, 104b and 104c indicate protection films or cover glass. The 104a is disposed above the display element 100a and protects the surface of the display element 100a. The 104b and 104c are disposed above the display elements 100b and 100c, and protect the surfaces of each of the display elements and are also able to act as insulators.
However, in a conventional layered form display medium like the one described above, there is the problem that the strength of the external terminal connection portions thereof is low. That is to say, in a conventional layered form display medium, since there are end portions of plural display elements stacked in a step shape, or since there are stacked end portions protruding out from each of the substrates, the strength is low at the boundary portion at the end portion of the joining portion(s) where an upper portion display element meets a lower portion display element, and there is the problem that when bending stress is applied to the joining end portion, the lead wiring lines that are present at the boundary portion may break.
Furthermore, electrical connection, between such a display medium and a relay substrate for external connection, must be undertaken for each of the display elements configuring the display medium, and the same number of relay substrates for external connection is required as the number of stacked display elements, and the problem arises that the production process thereof becomes complicated.
Recently, demand for display media that are flexible has risen, because of the ease of transporting and the portability of devices containing such display media. Such flexible display media usually use a flexible substrate of the order of several tens of μm to several hundreds of μm in thickness as the substrate. There is particular demand with flexible display media using flexible substrates for an increase in the strength of the external terminal connection portions thereof, but the present situation is that there is nothing yet available that meets such demands.